fix(install): correct gslt detection

lgsm/functions/command_install.sh

@@ -32,7 +32,7 @@ else
 
 	# Configuration.
 	install_config.sh
-	if [ -z "${gslt}" ]; then
+	if [ -v gslt ]; then
 		install_gslt.sh
 	elif [ "${shortname}" == "dst" ]; then
 		install_dst_token.sh